Many situations require the partial or total inversion of a bottle of liquid prior to pouring out the liquid contents. In many cases the contents are poured into a small opening, e.g. the addition of a lubricant to an engine crankcase through a relatively small opening without the use of a large funnel. Even when a funnel or pouring spout is used, lubricant often spills onto the engine or onto the ground which wastes product and creates a spill which must be remediated. Similar situations arise when adding brake fluid, transmission fluid, and coolant to fluid reservoirs.
Given the cost of many functional fluids and materials, especially synthetic lubricants, there is a high economic cost to the loss of product that when multiplied by the number of spills has a significant economic impact. The same is true for the environmental impact of spilled material that cannot be easily or cost effectively remediated. Moreover, the cost of labor in cleaning and remediating spills in the garage, at the worksite, and in the restaurant kitchen is also damaging due to lost economic opportunity.
The act of pouring a liquid from a bottle in a controlled manner to avoid spills is not without its challenges. As liquids are poured from an inverted bottle the pressure drops in the headspace of the bottle as the liquid leaves the bottle through the neck but is not replaced. The pressure differential between the headspace and the environment outside of the bottle eventually overcomes the force of gravity on the liquid pouring from the bottle and the flow is intermittently interrupted as air is drawn into the bottle to fill the headspace and equalize the pressure. The equilibrium across the system stays in flux and cycles between the increased pressure differential overcoming the force of gravity causing the pour and the decrease in the pressure differential resuming the flow.
Notably, several variables affect the rate of flow across the pour (e.g. viscosity, density, surface tension, etc.) and the end result is an ingestion of air across the top of the pour as an air channel is intermittently created. As air is added to the headspace, the pressure differential decreases but is in competition with the continuing increase of headspace causing the pressure differential to increase. The result is that the flow of liquid from an inverted bottle is turbulent because the ingestion of air back into the bottle is sporadic and results in a decrease in flow rate while air is ingested followed by increases in flow rate that manifest themselves as gushes of liquid. This turbulent flow results in the relative inability to control the flow of liquid from one point to another as it leaves the bottle's neck and results in spillage when trying to pour a liquid to a specific point.